Transceiver Architecture for Multiple Antenna Systems

ABSTRACT

A transceiver architecture with combined digital beamforming and analog/hybrid beamforming is proposed. Digital beamforming is used for beam training with reduced overhead (switching time). It is beneficial to estimate all UE&#39;s angle of arrival (AoA) at the same time. In addition, the pilot/training signals are transmitted in a narrow band to reduce complexity. Analog/hybrid beamforming is used for data transmission with high directive gain and low complexity. The value of beamforming weights (phase shifter values) in analog domain can be based on the estimation of AoA from beam training. By using digital beamforming for beam training, combined with analog/hybrid beamforming for data transmission, effective beamforming is achieved with reduced overhead, complexity, and cost.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 from U.S.Provisional Application No. 62/080,626, entitled “TransceiverArchitecture for Multiple Antenna Systems,” filed on Nov. 17, 2014; thesubject matter of which is incorporated herein by reference.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless communication,and, more particularly, to transceiver architecture with hybridbeamforming for multiple antenna systems.

BACKGROUND

The bandwidth shortage increasingly experienced by mobile carriers hasmotivated the exploration of the underutilized Millimeter Wave (mmWave)frequency spectrum between 3G and 300G Hz for the next generationbroadband cellular communication networks. The available spectrum ofmmWave band is two hundred times greater than the conventional cellularsystem. The mmWave wireless network uses directional communications withnarrow beams and can support multi-gigabit data rate. The underutilizedbandwidth of the mmWave spectrum has wavelengths ranging from 1 mm to100 mm. The very small wavelengths of the mmWave spectrum enable largenumber of miniaturized antennas to be placed in a small area. Suchminiaturized antenna system can produce high beamforming gains throughelectrically steerable arrays generating directional transmissions.

With recent advances in mmWave semiconductor circuitry, mmWave wirelesssystem has become a promising solution for real implementation. However,the heavy reliance on directional transmissions and the vulnerability ofthe propagation environment present particular challenges for the mmWavenetwork. In mmWave or high frequency systems, directional antenna isutilized to provide higher gain to compensate the pathloss. Directionalantenna can be implemented by phased array with many antenna elements.Beamforming and spatial multiplexing methods can be applied in multipleantenna systems. Analog, digital, or hybrid beamforming technique isused in phased array antenna systems. Channel state information isneeded when beamforming or spatial multiplexing is applied.

Channel state information can be obtained by estimating either uplink ordownlink pilot training symbols. In beamforming technique, angle ofarrival (AoA) is one of the channel state information. By adjusting thevalues of phase shifters, the beam direction in phased array systems canbe steered accordingly. In analog beamforming, a set of phase shiftervalues can be only applied in one training period. One specific antennapattern is associated with a set of phase shifter values. N trainingperiods are needed if N antenna patterns (directions) are to bedetected. This is time consuming. On the other hand, in digitalbeamforming, different phase shifter values can be applied by digitalsignal processing in one training period. Multiple RF chain is needed(NA antennas need NA RF chains), which results in high complexity.

A solution is sought to solve the problem of high data rate processingand high power consumption in digital beamforming as well as the problemof large overhead of switching time for switching beams in analog orhybrid beamforming.

SUMMARY

A transceiver architecture with combined digital beamforming andanalog/hybrid beamforming is proposed. Digital beamforming is used forbeam training with reduced overhead (switching time). It is beneficialto estimate all UE's angle of arrival (AoA) at the same time. Inaddition, the pilot/training signals are transmitted in a narrow band toreduce complexity. Analog/hybrid beamforming is used for datatransmission with high directive gain and low complexity. The value ofbeamforming weights (phase shifter values) in analog domain can be basedon the estimation of AoA from beam training. By using digitalbeamforming for beam training, combined with analog/hybrid beamformingfor data transmission, effective beamforming is achieved with reducedoverhead, complexity, and cost.

In one embodiment, a base station receives a plurality of data signalscarrying data symbols from a set of antenna elements in a beamformingcellular network. The base station performs analog beamforming toprocess the data symbols. The set of antenna elements are applied with afirst set of phase shift values via a set of phase shifters to form afirst antenna pattern to receive the plurality of data signals. The basestation receives a plurality of training signals carrying trainingsymbols from the set of antenna elements. The base station performsdigital beamforming to process the training symbols. The set of antennaelements are applied with a second set of phase shift values via abaseband processor to form a second antenna pattern to receive theplurality of training signals.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 illustrates combined digital beamforming for beam training withanalog/hybrid beamforming for data transmission in a beamformingcellular system in accordance with one novel aspect.

FIG. 2 is a simplified block diagram of a base station or a userequipment that carry out certain embodiments of the present invention.

FIG. 3 illustrates a first embodiment of a receiver with combineddigital beamforming and analog beamforming.

FIG. 4 illustrates a second embodiment of a receiver with combineddigital beamforming and hybrid beamforming.

FIG. 5 illustrates a third embodiment of a receiver with combineddigital beamforming and analog beamforming.

FIG. 6 illustrates a fourth embodiment of a receiver with combineddigital beamforming and hybrid beamforming.

FIG. 7 illustrates a fifth embodiment of a receiver with combineddigital beamforming and analog beamforming.

FIG. 8 illustrates a sixth embodiment of a receiver with combineddigital beamforming and hybrid beamforming.

FIG. 9 illustrates a seventh embodiment of a receiver with combineddigital beamforming and analog beamforming.

FIG. 10 illustrates an eighth embodiment of a receiver with combineddigital beamforming and hybrid beamforming.

FIG. 11 illustrates a ninth embodiment of a transmitter with combineddigital beamforming and analog beamforming.

FIG. 12 illustrates a tenth embodiment of a transmitter with combineddigital beamforming and hybrid beamforming.

FIG. 13 is a flow chart of a method of combined digital beamforming forbeam training with analog/hybrid beamforming for data transmission in abeamforming cellular system in accordance with one novel aspect.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 illustrates combined digital beamforming for beam training withanalog/hybrid beamforming for data transmission in a beamformingMillimeter Wave (mmWave) cellular network 100 in accordance with onenovel aspect. Beamforming mmWave mobile communication network 100comprises a base station BS 101 and a first user equipment UE 102 and asecond user equipment UE 103. The mmWave cellular network usesdirectional communications with narrow beams and can supportmulti-gigabit data rate. Directional communications are achieved viadigital (adaptive) and/or analog (switched) beamforming, whereinmultiple antenna elements are applied with multiple sets of beamformingweights (phase shift values) to form multiple beam patterns. In theexample of FIG. 1, BS 101 is directionally configured with multiplecells, and each cell is covered by a set of coarse TX/RX control beams.For example, cell 110 is covered by a set of four control beams CB1,CB2, cB3, and CB4. The collection of the control beams CB1-CB4 covers anentire service area of cell 110, and each control beam has a wider andshorter spatial coverage with smaller array gain. Each control beam inturn is covered by a set of dedicated data beams. For example, CB2 iscovered by a set of four dedicated data beams DB1, DB2, DB3, and DB4.The collection of the dedicated data beams covers a service area of onecontrol beam, and each dedicated data beam has a narrower and longerspatial coverage with larger array gain. Similarly, UE 102 and UE 103may also apply beamforming to from multiple beam patterns (#1 to #4).

Hierarchical level beam patterns is assumed in wireless or cellularnetworks. Level 0 beam pattern is omni-directional and used for macrocell stations. The set of control beams are lower-level (Level 1) beamsthat provide low rate control signaling to facilitate high rate datacommunication on higher-level (Level 2) dedicated data beams. The set ofcontrol beams may be periodically configured or occur indefinitely andrepeatedly in order known to the UEs. The set of control beams coversthe entire cell coverage area with moderate beamforming gain. Eachcontrol beam broadcasts minimum amount of cell-specific andbeam-specific information similar to System Information Block (SIB) orMaster Information Block (MIB) in LTE systems. The control beam anddedicated data beam architecture provides a robust control-signalingscheme to facilitate the beamforming operation in mmWave cellularnetwork systems.

Maintaining antenna pointing and tracking accuracy is essential in manyphases of the communication process. Beam administration mechanism,which includes both initial beam alignment and subsequent beam tracking,ensures that BS beam and UE beam are aligned for control and datacommunication. There are two types of beamforming: switched (analog orhybrid) beamforming and adaptive (digital) beamforming. The complexityof switched beam forming is low, while beam patterns are not flexibleand beam alignment time is long. The complexity of adaptive beamformingis high with flexible beam patterns, while beam alignment time isacceptable.

In according with one novel aspect, a transceiver architecture withcombined digital beamforming and analog/hybrid beamforming is proposed.Digital beamforming is used for beam training or beam administrationwith reduced overhead (switching time). It is beneficial to estimate allUE's angle of arrival (AoA) at the same time. In addition, thepilot/training signals are transmitted in a narrow band to reducecomplexity. Analog/hybrid beamforming is used for data transmission withhigh directive gain and low complexity. The value of beamforming weights(phase shifters) in analog domain can be based on the estimation of AoAfrom beam training. It is assumed that AoA information is coherent incertain bandwidth. Therefore, by using digital beamforming for beamtraining, combined with analog/hybrid beamforming for data transmission,effective beamforming is achieved with reduced overhead, complexity, andcost.

FIG. 2 is a simplified block diagram of a wireless device 201 thatcarries out certain embodiments of the present invention. Device 201 hasan antenna array 211 having multiple antenna elements that transmits andreceives radio signals, a receiver 230 comprising one or more RFtransceiver modules 231 and a baseband processing unit 232, coupled withthe antenna array, receives RF signals from antenna 211, converts themto baseband signal, and sends them to processor 233. RF transceiver 231also converts received baseband signals from processor 233, convertsthem to RF signals, and sends out to antenna 211. Processor 233processes the received baseband signals and invokes different functionalmodules to perform features in BS 201. Memory 234 stores programinstructions and data 235 to control the operations of device 201.Device 201 also includes multiple function modules that carry outdifferent tasks in accordance with embodiments of the current invention.

The functional modules are circuits that can be implemented andconfigured by hardware, firmware, software, and any combination thereof.For example, device 201 comprises a beam training circuit 220, whichfurther comprises a beamforming circuit 221, a beam monitor 222, and abeam training information circuit 223. Beamforming circuit 221 maybelong to part of the RF chain, which applies various beamformingweights to multiple antenna elements of antenna 211 and thereby formingvarious beams. Beam monitor 222 monitors received radio signals andperforms measurements of the radio signals over the various beams anddevice channel state information including AoA. Beam traininginformation circuit 223 provides beam training information includingtraining period, window size, and resource mapping information. Based onphased array reciprocity or channel reciprocity, the same receivingantenna pattern can be used for transmitting antenna pattern. Differentalgorithms can be applied in choosing the best receiving beam, including(but not limited to) power maximization, SINR maximization, orinterference minimization.

FIG. 3 illustrates a first embodiment of a receiver with combineddigital beamforming and analog beamforming. The receiver comprisescomponents for performing both digital beamforming and analogbeamforming. The digital beamformer comprises a plurality of antennascoupled with a plurality of low-noise amplifiers (LNAs), a plurality ofmixers, a plurality of narrow-band low-pass filters (NB-LPFs), aplurality of low-rate analog-to-digital converters (LR-ADCs), and abaseband processor 2. The analog beamformer comprises the plurality ofantennas coupled with the plurality of low-noise amplifiers (LNAs), aplurality of phase shifters, a signal combining circuit, a mixer, alow-pass filter (LPF), an analog-to-digital converter (ADC), and abaseband processor 1. In accordance with one novel aspect, for beamtraining, training symbols are transmitted in a narrow band and digitalbeamforming is applied. For high rate data transmission, data symbolsare transmitted in full band or subband and analog beamforming isapplied. Furthermore, beam-training symbols can be multiplexed with datasymbols in frequency domain and transmitted in the same training periodand processed simultaneously.

For beam training, the receiver receives a plurality of narrow bandtraining signals carrying training symbols via N antennas. Each trainingsignal follows the digital beamforming paths PD-1 to PD-N as depicted bythe dotted lines. Taking path PD-1 as an example, the training signal isfirst received by an antenna 301 and passed through an LNA 302. AfterLNA process, signal T1 is down-converted by a mixer 303 and then passedthrough a narrow-band LPF 304 and low-rate ADC 305 to obtain anarrow-band digital signal B1. The narrow-band digital signals B1through BN are utilized by baseband processor 312, which performs signalcombination and performs digital beamforming or estimating angle ofarrival information.

Using digital beamforming method can be beneficial to estimate differentUEs' angle of arrival information at the same time. If training symbolsof all UEs can be distinguished in spatial or time or frequency or codedomain, then the beam administration can be done in one training period.Typically, digital beamforming requires high data rate processing andhigh complexity. For example, the base station needs to process 128 GHzdata when 64 antenna elements with 1 GHz signals are applied. However,by receiving training signals in a narrow band, e.g., one narrowband=1/64 full band, the based station only needs to process 2 GHz datawhen 64 antenna elements with 1/64 GHz training signals are applied.This way, hardware complexity is reduced.

For high rate data transmission, the receiver receives a plurality ofdata signals R1 through RN carrying data symbols via the N antennas.Each data signal follows the analog beamforming paths PA-1 to PA-N asdepicted by the dashed lines. Taking PA-1 as an example, the data signalR1 is first received by an antenna 301 and passed through an LNA 302.After LNA process, the signal is applied with a phase shifter 306 foroutputting signal S1. Signals S1 through SN are then combined by acombining circuit 307. The combined analog signal SC is down-convertedby a mixer 308 and then passed through an LPF 309 and an ADC 310 toobtain a digital signal A1. The digital signal A1 is utilized bybaseband processor 311, which performs analog beamforming.

In analog beamforming, a set of phase shifter values can be only appliedin one training period. One specific antenna pattern is associated witha set of phase shift values. The simplest way to adjust the set of phaseshift values is via switched beam method. If N antenna patterns are tobe detected, then N training periods are needed. As a result, analogbeamforming is time consuming (long switching time) if used for beamtraining or beam administration. However, for data transmission, analogbeamforming can be utilized to effectively reduce hardware complexity.The values of the phase shifters can be adjusted according to theestimated AoA information from past beam training symbols.

FIG. 4 illustrates a second embodiment of a receiver with combineddigital beamforming and hybrid beamforming. FIG. 4 is similar to FIG. 3.In the example of FIG. 4, the N antenna elements are grouped intomultiple of L groups. For beam training, similar to FIG. 3, trainingsignals follow digital beamforming paths, e.g., PD-1, and are processedby baseband processor 2. For data transmission, data signals followanalog/hybrid beamforming paths, e.g., PA-1, and are processed bybaseband processor 1. In analog/hybrid beamforming, data signals frommultiple analog paths PA-1 through PA-L (G1 through GL) are combined andprocessed together by baseband processor 1 using digital beamforming.The hybrid beamforming can be used for MU-MIMO data transmission. Forexample, each group of RF chains used for analog beamforming isassociated with the data transmission of a different UE.

FIG. 5 illustrates a third embodiment of a receiver with combineddigital beamforming and analog beamforming. The receiver comprisescomponents for performing both digital beamforming and analogbeamforming. The receiver comprises a plurality of antennas (501)coupled with a plurality of low-noise amplifiers (LNA 502), a pluralityof phase shifters (511), a first set of switches C1 to CN, a signalcombining circuit 521, a mixer 522, a narrow-band low-pass filter(NB-LPF) 523, a low-rate analog-to-digital converter (LR-ADC) 524, anLPF 525, an ADC 526, a second set of switches D1 and D2, and a basebandprocessor 530. For beam training, training symbols are transmitted in anarrow band and digital beamforming is applied. For high rate datatransmission, data symbols are transmitted in full band or subband andanalog beamforming is applied.

In the example of FIG. 5, either beamforming for beam training or fordata transmission can be applied simultaneously. A specific period andnarrow band training signals are transmitted for beam training. Duringthe specific period, full band data transmission cannot be operated.Assume there are N antennas, N LNAs, and N phase shifters. For example,a first signal R1 is received by antenna 501 and passes through LNA 502for outputting signal T1. Signal T1 after LNA 502 can select passingphase shifter 511 for analog beamforming or omitting for digitalbeamforming. Note that for digital beamforming, the value of phaseshifter 511 can be one (i.e., zero phase). Switches D1 and D2 controlwhether analog or digital beamforming is applied.

If D1 is on, then digital beamforming is applied. The timing of the setof switches C1 to CN are serialized in time domain. At a given timeslot, each received narrow band training signal passes through acorresponding antenna, LNA, omits the phase shifter and then reaches thesignal combining circuit 521. The combined signal SC is thendown-converted by mixer 522 and then passed through narrow-band LPF 523and low-rate ADC 524 to obtain narrow-band digital signals. Thenarrow-band digital signals are utilized by baseband processor 530,which performs signal combination and performs digital beamforming orestimating AoA information. Note that because each narrow-band trainingsignal is sequentially processed, only one NB-LPF and one LR-ADC areneeded as compare to N NB-LPFs and N LR-ADCs are needed in FIG. 3.

If D2 is on, then analog beamforming is applied. The set of switches C1to CN are turned on simultaneously. Each received wide-band data signalpasses through a corresponding antenna, LNA, and phase shifter and thenreaches the signal combining circuit 521. The combine signal SC is thendown-converted by mixer 522 and then passed through LPF 525 and ADC 526to obtain a wide-band digital signal. The wide-band digital signal isutilized by baseband processor 530, which performs analog beamforming.Further, note that the LPF 525 and ADC 526 in dashed box 520 can bere-configured as NB-LPF 523 and LR-ADC, respectively. As a result, onlyone LPF and one ADC are needed.

FIG. 6 illustrates a fourth embodiment of a receiver with combineddigital beamforming and hybrid beamforming. FIG. 6 is similar to FIG. 5.In the example of FIG. 6, the N antenna elements are grouped intomultiple of L groups. For beam training, narrowband training signalsfollow digital beamforming paths when D1 is on. For data transmission,wideband data signals follow analog/hybrid beamforming paths when D2 ison. In analog/hybrid beamforming, data signals from multiple analogpaths are combined and processed together by baseband processor 530using digital beamforming. The hybrid beamforming can be used forMU-MIMO data transmission. For example, each group of RF chains used foranalog beamforming is associated with the data transmission of adifferent UE.

FIG. 7 illustrates a fifth embodiment of a receiver with combineddigital beamforming and analog beamforming. FIG. 7 is an alternative ofFIG. 3. The receiver comprises components for performing both digitalbeamforming and analog beamforming. The digital beamformer comprises aplurality of antennas coupled with a plurality of low-noise amplifiers(LNAs), a plurality of mixers, a plurality of narrow-band low-passfilters (NB-LPFs), a mux, an analog-to-digital converter (ADC2), and abaseband processor 2. The analog beamformer comprises the plurality ofantennas coupled with the plurality of low-noise amplifiers (LNAs), aplurality of phase shifters, a signal combining circuit, a mixer, alow-pass filter (LPF), an analog-to-digital converter (ADC1), and abaseband processor 1. In accordance with one novel aspect, for beamtraining, training symbols are transmitted in a narrow band and digitalbeamforming is applied. For high rate data transmission, data symbolsare transmitted in full band or subband and analog beamforming isapplied. Furthermore, beam-training symbols can be multiplexed with datasymbols in frequency domain and transmitted in the same training periodand processed simultaneously.

The digital and analog beamforming paths of FIG. 7 are similar to thedigital and analog beamforming paths of FIG. 3. In the example of FIG.7, however, the digital beamforming path includes a set of sequentialhigh-rate switches C1 to CN as depicted. Under the control of theswitches, each narrowband training signal sequentially passes througheach NB-LPF, and are multiplexed in time domain by mux 711. The resultedanalog signal M1 is then converted to a digital signal B1 by ahigher-rate ADC2. Digital signal B1 is then utilized by basebandprocessor 2, which performs digital beamforming or estimating angle ofarrival information. Instead of having a plurality of low-rate ADCs inFIG. 3, FIG. 7 has only one higher-rate ADC2 for digital beamforming.

FIG. 8 illustrates a sixth embodiment of a receiver with combineddigital beamforming and hybrid beamforming. FIG. 8 is similar to FIG. 7.In the example of FIG. 8, the N antenna elements are grouped intomultiple of L groups. For beam training, similar to FIG. 7, trainingsignals follow digital beamforming paths and are processed by basebandprocessor 2. For data transmission, data signals follow analog/hybridbeamforming paths and are processed by baseband processor 1. Inanalog/hybrid beamforming, data signals from multiple analog paths G1 toGL are combined and processed together by baseband processor 1 usingdigital beamforming. The hybrid beamforming can be used for MU-MIMO datatransmission. For example, each group of RF chains used for analogbeamforming is associated with the data transmission of a different UE.

FIG. 9 illustrates a seventh embodiment of a receiver with combineddigital beamforming and analog beamforming. FIG. 9 is an alternative ofFIG. 7. The digital and analog beamforming paths of FIG. 9 are similarto the digital and analog beamforming paths of FIG. 7. In the example ofFIG. 9, however, each narrowband training signal sequentially passesthrough each switch C1 to CN in time domain and combined as signal M1.Signal M1 is then down-converted by a mixer 911 and then passed througha narrow-band NB-LPF 912 and ADC2 to obtain a digital signal B1. Thedigital signals B1 is utilized by baseband processor 2, which performsdigital beamforming or estimating angle of arrival information. Insteadof having a plurality of NB-LPFs in FIG. 7, FIG. 9 has only one NB-LPFto reduce hardware complexity.

FIG. 10 illustrates an eighth embodiment of a receiver with combineddigital beamforming and hybrid beamforming. FIG. 10 is similar to FIG.9. In the example of FIG. 10, the N antenna elements are grouped intomultiple of L groups. For beam training, similar to FIG. 9, trainingsignals follow digital beamforming paths and are processed by basebandprocessor 2. For data transmission, data signals follow analog/hybridbeamforming paths and are processed by baseband processor 1. Inanalog/hybrid beamforming, data signals from multiple analog paths G1 toGL are combined and processed together by baseband processor 1 usingdigital beamforming. The hybrid beamforming can be used for MU-MIMO datatransmission. For example, each group of RF chains used for analogbeamforming is associated with the data transmission of a different UE.

FIG. 11 illustrates a ninth embodiment of a transmitter with combineddigital beamforming and analog beamforming. The transmitter of FIG. 11is corresponding to the receiver of FIG. 3. The transmitter comprisescomponents for performing both digital beamforming and analogbeamforming. The digital beamformer comprises a baseband processor 2, aplurality of low-rate digital-to-analog converters (LR-DACs), aplurality of narrow-band low-pass filters (NB-LPFs), a plurality ofmixers, and a plurality of antennas coupled with a plurality of poweramplifiers (PAs). The analog beamformer comprises a baseband processor1, a DAC, an LPF, a mixer, a plurality of phase shifters, and theplurality of antennas coupled with the plurality of power amplifiers(PAs). In accordance with one novel aspect, for beam training, trainingsymbols are transmitted in a narrow band and digital beamforming isapplied. For high rate data transmission, data symbols are transmittedin full band or subband and analog beamforming is applied. Furthermore,beam-training symbols can be multiplexed with data symbols in frequencydomain and transmitted in the same training period and processedsimultaneously.

For beam training, the transmitter transmits a plurality of narrow bandtraining signals carrying training symbols via N antennas. Takingdigital beamforming path PD-1 as an example, baseband processor 2performs digital beamforming by applying phase shifter values andamplitude adjustments on a narrow-band training signal T1. Signal T1 isfirst converted to analog signal by LR-DAC 1101 and then passed throughNB-LPF 1102, up-converted by a mixer 1103, and finally passed through PA1104 to be transmitted via antenna 1105.

Typically, digital beamforming requires high data rate processing andhigh complexity. For example, the base station needs to process 128 GHzdata when 64 antenna elements with 1 GHz signals are applied. However,by transmitting training signals in a narrow band, e.g., one narrowband=1/64 full band, the based station only needs to process 2 GHz datawhen 64 antenna elements with 1/64 GHz training signals are applied.This way, hardware complexity is reduced.

For high rate data transmission, the transmitter transmits full band orsubband data signals carrying data symbols via N antennas. Taking analogbeamforming path PA-1 as an example, a data signal R1 is first generatedby baseband processor 1. Signal R1 is converted to analog signal by DAC1111, passed through LPF 1112, up-converted by a mixer 1113, thenapplied with a phase shifter 1114, and finally passed through PA 1104 tobe transmitted by antenna 1105.

In analog beamforming, a set of phase shifter values can be only appliedin one training period. One specific antenna pattern is associated witha set of phase shift values. The simplest way to adjust the set of phaseshift values is via switched beam method. If N antenna patterns are tobe detected, then N training periods are needed. As a result, analogbeamforming is time consuming (long switching time) if used for beamtraining or beam administration. However, for data transmission, analogbeamforming can be utilized to effectively reduce hardware complexity.The values of the phase shifters can be adjusted according to theestimated AoA information from past beam training symbols.

FIG. 12 illustrates a tenth embodiment of a transmitter with combineddigital beamforming and hybrid beamforming. FIG. 12 is similar to FIG.11. In the example of FIG. 12, the N antenna elements are grouped intomultiple of L groups. For beam training, similar to FIG. 11, trainingsignals are processed by baseband processor 2 and follow digitalbeamforming paths. For data transmission, data signals are processed bybaseband processor 1 and follow analog/hybrid beamforming paths. Inanalog/hybrid beamforming, data signals are processed together bybaseband processor 1 using digital beamforming and then follow multipleanalog paths. The hybrid beamforming can be used for MU-MIMO datatransmission. For example, each group of RF chains used for analogbeamforming is associated with the data transmission of a different UE.

FIG. 13 is a flow chart of a method of combined digital beamforming forbeam training with analog/hybrid beamforming for data transmission in abeamforming cellular system in accordance with one novel aspect. In step1301, a base station receives a plurality of data signals carrying datasymbols from a set of antenna elements in a beamforming cellularnetwork. In step 1302, the base station performs analog beamforming toprocess the data symbols. The set of antenna elements are applied with afirst set of phase shift values via a set of phase shifters to form afirst antenna pattern to receive the plurality of data signals. In step1303, the base station receives a plurality of training signals carryingtraining symbols from the set of antenna elements. In step 1304, thebase station performs digital beamforming to process the trainingsymbols. The set of antenna elements are applied with a second set ofphase shift values via a baseband processor to form a second antennapattern to receive the plurality of training signals.

Although the present invention has been described in connection withcertain specific embodiments for instructional purposes, the presentinvention is not limited thereto. Accordingly, various modifications,adaptations, and combinations of various features of the describedembodiments can be practiced without departing from the scope of theinvention as set forth in the claims.

What is claimed is:
 1. A method comprising: receiving a plurality ofdata signals carrying data symbols by a base station from a set ofantenna elements in a beamforming cellular network; performing analogbeamforming to process the data symbols, wherein the set of antennaelements are applied with a first set of phase shift values via a set ofphase shifters to form a first antenna pattern to receive the pluralityof data signals; receiving a plurality of training signals carryingtraining symbols by the base station from the set of antenna elements;and performing digital beamforming to process the training symbols,wherein the set of antenna elements are applied with a second set ofphase shift values via a baseband processor to form a second antennapattern to receive the plurality of training signals.
 2. The method ofclaim 1, wherein the training symbols and the data symbols aremultiplexed in frequency domain and processed simultaneously.
 3. Themethod of claim 1, wherein each data signal occupies a wideband, andwherein each training signal occupies a narrow band.
 4. The method ofclaim 1, wherein the training symbols are utilized for estimating anangle of arrival (AoA) of a transmitting device.
 5. The method of claim4, wherein the base station estimate AoA information of multipletransmitting devices simultaneously.
 6. The method of claim 4, whereinthe phase shift values of the phase shifters are determined based on theestimated AoA of the transmitting device.
 7. The method of claim 1,wherein each training signal passes through a narrowband low pass filter(NB-LPF) and a low-rate analog-to-digital converter (LR-ADC) to beprocessed by the baseband processor.
 8. The method of claim 1, whereinthe training symbols and the data symbols are processed separately intime domain controlled by a set of switches.
 9. The method of claim 1,wherein the plurality of training signals is processed sequentially intime domain controlled by a set of switches.
 10. The method of claim 9,wherein the plurality of training signals is processed by a single lowpass filter and/or a single analog-to-digital converter.
 11. The methodof claim 1, wherein the data symbols are grouped into a number of groupsto be processed by a combination of analog beamforming and digitalbeamforming.
 12. A wireless device, comprising: a plurality of antennaelements that receives a plurality of data signals carrying data symbolsin a beamforming cellular network, wherein the plurality of antennaelements also receives a plurality of training signals carrying trainingsymbols; a first baseband processor that performs analog beamforming toprocess the data symbols, wherein the antenna elements are applied witha first set of phase shift values via a set of phase shifters to form afirst antenna pattern to receive the plurality of data signals; and asecond baseband processor that performs digital beamforming to processthe training symbols, wherein the antenna elements are applied with asecond set of phase shift values via the second baseband processor toform a second antenna pattern to receive the plurality of trainingsignals.
 13. The device of claim 12, wherein the training symbols andthe data symbols are multiplexed in frequency domain and processedsimultaneously.
 14. The device of claim 12, wherein each data signaloccupies a wideband, and wherein each training signal occupies a narrowband.
 15. The device of claim 12, wherein the training symbols areutilized for estimating an angle of arrival (AoA) of a transmittingdevice.
 16. The device of claim 15, wherein the base station estimateAoA information of multiple transmitting devices simultaneously.
 17. Thedevice of claim 15, wherein the phase shift values of the phase shiftersare determined based on the estimated AoA of the transmitting device.18. The device of claim 12, wherein each training signal passes througha narrowband low pass filter (NB-LPF) and a low-rate analog-to-digitalconverter (LR-ADC) to be processed by the second baseband processor. 19.The device of claim 12, wherein the training symbols and the datasymbols are processed separately in time domain controlled by a set ofswitches.
 20. The device of claim 12, wherein the plurality of trainingsignals is processed sequentially in time domain controlled by a set ofswitches.
 21. The device of claim 20, wherein the plurality of trainingsignals is processed by a single low pass filter and/or a singleanalog-to-digital converter.
 22. The device of claim 12, wherein thedata symbols are grouped into a number of groups to be processed by acombination of analog beamforming and digital beamforming.